1. Field of the Invention
The present invention relates to an optical amplifier, an optical amplifying system, a wavelength converter, an optical amplification method, and an optical communication system using the same.
2. Description of the Related Art
In optical communication, optical amplifiers have become indispensable. In current optical communication systems, as optical amplifiers or optical amplifying systems for optical communication band, erbium-doped fiber amplifiers (EDFA), Raman amplifiers, or Raman amplifying systems have been put into practice.
On the other hand, an optical parametric amplifier (OPA), as disclosed in Japanese Patent Application Laid-open No. 2008-89781, which makes use of nonlinear effect in an optical fiber for optical amplification, has not been put into practice. One major reason for not having been made into practice is considered because amplification band is narrow or a gain spectrum is not flat. It should be noted that an OPA is used also as a wavelength converter. In addition, as an optical amplifier making use of nonlinear effect in an optical fiber, there is a phase-sensitive optical amplifier (PSA).